1. Field of the Invention
The present invention relates to an inductive coupling transmitting and receiving apparatus.
2. Description of the Related Art
Recently, inductive coupling communications has come into the spotlight as new local area contactless communications. In conventional local area contactless communications such as radio frequency identification (RFID), a frequency band mainly used is a high frequency of 800 MHz to 2.4 GHz, and therefore, power consumption is so high. RFID using a low frequency of 13.56 MHz has a very low data transfer rate of a few tens to a few hundreds of Kbps. On the other hand, in the inductive coupling communications, its data transfer rate is in a very wide range of a few Kbps to a few Gbps, and a data transfer rate of more than a few Mbps can be maintained in despite of its low frequency of about 13.56 MHz.
In such inductive coupling communications, its application area has been expanded to all electronics industries. For example, the inductive coupling communications is applicable to application areas in which an inductor has a fixed inductance, i.e., application areas used in testing chips manufactured using an inductor formed on a chip in large quantities, in communications between chips stacked in a layer structure, in testing circuit boards manufactured/assembled, in data communications, and the like.
In inductive coupling communications, an inductor generally has a fixed inductance. This is because the inductor is solid and stable by being formed in a chip or made of a metal. However, as a conventional art for incorporating an electronic circuit in a flexible material has recently been developed, the inductance of an inductor may not be fixed. For example, the inductor may include an inductor formed in printable electronics, e.g., on a printed circuit board, or an inductor formed of a conductive fabric on cloth. In this case, inductance is varied depending on temporal/spatial changes. Therefore, it is difficult to perform communications having stability and a low error rate.
A conventional phase locked loop (PLL) circuit may be applied to compensate the variation of inductance. However, in the conventional PLL circuit, a waveform outputted from a phase-frequency detector passes through a low pass filter (LPF) and is then converted into a specific digital level by inputting the outputted waveform to an analog-to-digital converter (ADC) via a charge pump. After that, a value of a capacitor bank is adjusted by analyzing the digital level. As such, the conventional PLL circuit uses such a complicated method in which power consumption is very high. This is because the conventional PLL circuit uses “a continuous frequency signal” while its phase and frequency are fixed. For this reason, a precise and stable loop should be formed in the conventional PLL circuit. Therefore, the conventional art uses a complicated device, despite of inefficiency in its power consumption and area occupation.